It is conventional in the art to produce mineral fiber sheets and batts by gluing together a stack of mineral fibers into a sheet by using binders, such as phenolic resin. A mineral fiber sheet produced by such a technique is relatively stiff. If it is to be fitted in between rafters spaced apart by variable distances, this cannot be done by simply compressing the sheets, at least not if the differences in spacing, as is usually the case, amount to more than 1 to 2 cm. In that case, the mineral fiber sheets must be cut to size, accordingly, which requires a considerable expenditure of time and labor and wastes material. Another disadvantage that a relatively large amount of mineral dust is produced when the mineral fiber sheets are cut to size. It has therefore already been proposed, in German Patent Document A 32 03 622, Conrad et al, to work the peripheral regions of the mineral fiber sheet or batt in such a way that the fibrous composite structure is at least partly disintegrated. This is intended to create a compressible zone that makes it possible to fit the mineral fiber sheet between rafters even when the rafters are spaced apart from one another by up to about 5 cm less than the width of the mineral fiber sheet. For working the peripheral region, the use of pressure rollers located in pairs at an acute angle to the center plane of the mineral fiber sheet or batt, so that they enclose the peripheral region between them, is proposed. However, the method has not proved successful and therefore never gained commercial acceptance. One disadvantage of the method is that it does not enable uniform separation of the fibrous composite structure. In the manufacture of a mineral fiber sheet or batt, certain nonuniformities must always be expected, which then become problematic during fulling. In the resultant product, the fulled zone is variably compressible. Such variations in compressibility can be a considerable hindrance to installing the sheet or batt, or can even make it impossible. Insulating sheets prepared in the manner described have a tendency to buckle laterally outward in the deformed region and then to fall out between the rafters again during or after installation.
The Conrad et al German Patent Document A 32 03 622 also proposes, in passing, replacing the pressure rollers with one or more press plates, which are connected to a drive mechanism to generate a reciprocating motion or a pivoting motion. If the fulling is done with a press plate acting laterally upon the mineral fiber batt, then the mineral fiber batt is compressed over its entire width. This has the disadvantage that the fibrous composite structure is loosened over the entire width. This loosening is relatively slight, so that a strong force is necessary to install the plate between the rafters. On the other hand, the loosening of the fibrous composite structure over its entire width also has the effect that upon being installed, the mineral fiber sheet has a tendency to sag. It is accordingly unsurprising that the known method has not found any practical application.